1. Field of the Invention
This invention relates to a device for cleaning, by a scouring or scrubbing action, the inner surface of a tube, a tubular film, such as a tubular, semipermeable membrane used for reverse osmosis or ultrafiltration separation operations, or heat exchanger tubes. The present device enables a resilient sponge ball or the like scrubbing element, hereafter referred to as a scrubbing element, to be easily inserted into and removed from a piping system.
2. Description of the Prior Art
It is well-known that substances suspended or dissolved in liquids may be deposited on the inner surfaces of tubular semipermeable membranes of reverse osmosis and ultrafiltration apparatuses, and also on the inner surfaces of heat exchanger tubes, thus resulting in a lowered efficiency of the apparatus or heat exchanger. In order periodically to remove these deposits, scrubbing elements are introduced into the piping system and are moved therethrough, with the liquid. In the prior art such as disclosed in U.S. Pat. No. 3,819,513, mesh screens are provided at both ends of the piping system. The scrubbing elements are interposed between these screens and are moved back and forth through the piping system by alternating the direction of the liquid flow through the piping system. In this prior apparatus, the scrubbing elements are contained at all times in the piping system. According to a further apparatus shown in Japanese Utility Model application No. 0153343 of 1974, the piping system is fitted with valve means for the scrubbing device and the scrubbing elements are introduced into and taken out from the piping system for each scrubbing operation. These known apparatuses have their advantages and disadvantages. With the first-mentioned apparatus, the screens must be removed for insertion and removal of the scrubbing elements. The flow of the liquid must be discontinued or the liquid must be conducted through a separate piping system during such change-over time. When the scrubbing elements are subjected to considerable wear by the scrubbing operation, the removal operation must be carried out frequently. Moreover, when the scrubbing elements have been subjected to chemical deterioration and/or physical soiling (hereafter referred to, in general, as deterioration), such as when the piping system is being sterilized, the scrubbing elements must be taken out from the piping system. On the other hand, the first-mentioned apparatus has the advantage that the regular operation and the scrubbing can be performed for an extended time with the scrubbing elements remaining in the piping system, provided that the scrubbing elements are subjected to a smaller degree of deterioration so that they remain effective for scrubbing. Moreover, the direction of the flow of the liquid through the piping system can be reversed easily by providing suitable by-pass and valve means. Hence the device can be automated without much difficulty to achieve more efficient scrubbing operation. The apparatus of the second-mentioned type has the advantage that the insertion and removal of the scrubbing elements may be facilitated by the provision of the valve means which overcomes the disadvantages inherent in the first-mentioned apparatus. However, the scrubbing elements must be inserted and removed for each scrubbing operation even though they otherwise could be allowed to remain in the piping system for an extended time. Turning to the structural aspects, with the first-mentioned system, it is necessary to provide mesh screens in at least two places in the piping system and special piping and valve means for reversing the liquid flow direction. This means that a special operation for effecting scrubbing will become necessary regardless of whether the operation is carried out manually or automatically. Moreover, when the flow direction is such that the scrubbing elements are forcibly pressed against the surrounding screen, the scrubbing elements will partially block the piping system and special means must be provided to reduce the resulting increased resistance to the flow of the liquid. Under these circumstances, the device becomes complicated in structure and more costly. With the second-mentioned apparatus as disclosed for instance in Japanese Utility Model publication No. 0153343/1974, the scrubbing element is inserted into and removed from the piping system by special valve means which are rather similar to the commonly marketed ball cocks. The ball cock housing has to be provided with three or four ports and the valve body should be fitted with a special saucer. The valve means are therefore not of the commercially available type, although they are similar in structure to the conventional ball cocks. A specialized manufacturing technique is usually involved in the manufacture of ball cocks for this special purpose. Thus, these valve means are expensive. These valve means are manufactured with a high degree of precision and, when they are obtained by remodelling commercially available devices, may give rise to leakage or operational difficulties due to the strain caused by the hot machining operation. In operation, when the valve means are revolved for insertion or removal of the scrubbing elements, the flow of the liquid must be discontinued temporarily which may cause severe danger. It may be envisaged to provide a by-pass means in the valve body, but such measures are almost impossible with the ball cocks from the structural and machining points of view and, therefore, special by-pass means must be provided in addition to the valve means.